Focused-Pulsed sludge pre-treatment increases the bacterial diversity and relative abundance of acetoclastic methanogens in a full-scale anaerobic digester.

The low yield of methane in anaerobic digestion systems represents a loss of energy that can be captured as renewable energy when the input sludge is pre-treated to make it more bioavailable. We investigated Focused-Pulsed (FP) pre-treatment, which make complex biological solids more bioavailable by exposing them to rapid pulses of a very strong electric field. We investigated how the microbial ecology in full-scale anaerobic digesters was altered when the digesters' methane production rate was significantly increased by FP pre-treatment. Using clone libraries and quantitative PCR, we demonstrated a shift in methanogenic genera to the acetate-cleaving Methanosaeta and away from the H(2)-oxidizing Methanoculleus. In addition, the acetate concentration in the effluent was very low, probably due to the dominance of Methanosaeta, which are capable of scavenging low acetate concentrations. By analyzing 36,797 pyrosequencing tags from the V6 region of the bacterial 16S rRNA gene, along with archaeal and bacterial clone libraries and quantitative PCR, we compared the microbial community composition before and after FP treatment. The bacterial community became more diverse after FP pre-treatment and was populated more by phylotypes associated with cellulose fermentation (Ruminococcus), scavenging of biomass-derived organic carbon (Chloroflexi), and homo-acetogenesis (Treponema). We interpret that, as the overall activity of the community was stimulated by addition of more bioavailable organic matter, the bacterial community became more phylogenetically diverse to take advantage of the added input of biodegradable material and in response to the more efficient utilization of acetate by Methanosaeta.

Full-scale application of focused-pulsed pre-treatment for improving biosolids digestion and conversion to methane.

We tested at full-scale the innovative Focused Pulsed (FP) technology for pre-treating waste sludge in order to improve methane gas production and biosolids reduction in sludge digestion, but without incurring problems of odors, toxicity, and high costs for chemical or energy consumption. FP pre-treatment of a mixture of primary and secondary sludge increased the soluble COD by 160% and DOC 120% over the control. FP pre-treatment of 63% of the input waste sludge increased biogas production by over 40% and reduced biosolids requiring disposal by 30% when compared to the plant baseline. FP pre-treatment also correlated with a shift of the bacterial and archaeal communities. The most significant change was that the acetate-cleaving Methanosaeta became the dominant methanogen. Full FP pre-treatment should increase biogas production and biosolids removal by 60% and 40%, respectively. Full FP pre-treatment should generate energy benefits of at least 2.7 times and as high as 18 times the FP energy input, depending on heat recovery from FP treatment. For a plant treating 76,000 m3/d of wastewater (380 m3-sludge/d), FP treatment should generate an annual economic benefit of approximately $540,000 net of electricity and other operating and maintenance costs. This represents a payback period of three years or less.

Reduction of Np(V) and precipitation of Np(IV) by an anaerobic microbial consortium.

A combination of experimental, analytical, and modeling investigations shows that an anaerobic, sulfate-reducing consortium reduced Np(V) to Np(IV), with subsequent precipitation of a Np(IV) solid. Precipitation of Np(IV) during growth on pyruvate occurred before sulfate reduction began. H2 stimulated precipitation of Np(IV) when added alone to growing cells, but it slowed precipitation when added along with pyruvate. Increasing concentrations of pyruvate also retarded precipitation. Accumulation of an intermediate pyruvate-fermentation product--probably succinate--played a key role in retarding Np(IV) precipitation by complexing the Np(IV). Hydrogen appears to have two roles in controlling Np precipitation: donating electrons for Np(V) reduction and modulating intermediate levels. That Np(V) is microbially reduced and subsequently precipitated under anaerobic conditions has likely beneficial implications for the containment of Np on lands contaminated by radionuclides, but complexation by fermentation intermediates can prevent immobilization by precipitation.

Mathematical modeling of precipitation and dissolution reactions in microbiological systems.

We expand the biogeochemical model CCBATCH to include a precipitation/dissolution sub-model that contains kinetic and equilibrium options. This advancement extends CCBATCH's usefulness to situations in which microbial reactions cause or are affected by formation or dissolution of a solid phase. The kinetic option employs a rate expression that explicitly includes the intrinsic kinetics for reaction or mass-transport control, the difference from thermodynamic equilibrium, and the aqueous concentration of the rate-limiting metal or ligand. The equilibrium feature can be used alone, and it also serves as check that the kinetic rate never is too fast and "overshoots" equilibrium. The features of the expanded CCBATCH are illustrated by an example in which the precipitation of Fe(OH)3(s) allows the biodegradation of citric acid, even though complexes are strong and not bioavailable. Precipitation releases citrate ligand, and biodegradation of the citrate increases the pH.